The Mg2+ transporter CNNM4 regulates sperm Ca2+ homeostasis and is essential for reproduction

Abstract

Ca2+ influx triggers sperm capacitation; however, the underlying regulatory mechanisms remain incompletely understood. Here, we show that CNNM4, a Mg2+ transporter, is required for Ca2+ influx during capacitation. We find that Cnnm4-deficient male mice are almost infertile because of sperm dysfunction. Motion analyses show that hyperactivation, a qualitative change in the mode of sperm motility during capacitation, is abrogated in Cnnm4-deficient sperm. In contrast, tyrosine phosphorylation of flagellar proteins, a hallmark of capacitation, is excessively augmented. These seemingly paradoxical phenotypes of Cnnm4-deficient sperm are very similar to those of sperm lacking a functional cation channel of sperm (CatSper) channel, which plays an essential role in Ca2+ influx during sperm capacitation. Ca2+ imaging analyses demonstrate that Ca2+ influx is perturbed in Cnnm4-deficient sperm, and forced Ca2+ entry into these sperm normalizes the level of tyrosine phosphorylation. Furthermore, we confirm the importance of CNNM4 in sperm by generating germcell- specific Cnnm4-deficient mice. These results suggest a new role of CNNM4 in sperm Ca2+ homeostasis.